1. Field of the Invention
The present invention generally relates to multiple-section aerial ladders and particularly to an aerial ladder roller assembly to improve the function of the ladder during extension and retraction of ladder sections.
2. Discussion of Related Art
A common problem in the extension of telescoping ladders, especially very large ladders, such as aerial ladders found on fire trucks, is the slipping, sticking, and surging that may occur during the extension and retraction of the ladder sections. Ladder sections typically follow tracks or slides that require a high degree of maintenance through regular greasing to reduce the defects cited above. Otherwise, the surging motion reduces the life of cables used to extend and retract ladder sections due to the dynamic loads encountered. Since dependability in fire truck aerial ladders is essential, there has been a resistance in the art to cure these problems.
One possible solution to the problems is the use of roller assemblies at contact points of the ladder sections. No successful such roller assemblies are known in the art most likely because such application would need to be highly dependable yet easily maintained. Further, single metal rollers have not been successful due to line contacts between the ladder rail and the roller causing high stresses and distortion of the base rails of the ladder.
Rollers attached to ladders are known in the art, but not for the solution of problems cited above. For example, U.S. Pat. No. 4,754,843 to Anderson discloses a roller assembly attached to the top of a ladder to assist in ladder increasing and decreasing inclination. A similar device is also found in U.S. Pat. No. 5,123,503 to Clarke. U.S. Pat. No. 5,226,703 to Norman discloses the use of rollers to facilitate movement of “endless tracks” in large construction equipment, but only for support rollers. U.S. Pat. No. 5,172,952 to Lasnetski also discloses the use of rollers on ladders but only to assist in storing the ladder. Here a roller is placed at the end of the ladder to roll on a track suspended from the ceiling of a truck. The roller is not integral to a slide mechanism and is not designed to support a load on the ladder while in use.
Thus, there is a desire and need in the art to provide a dependable and easily maintainable roller assembly integral to the slide tracks of a multi-section ladder.